Contractile Responses of Canine Tracheal Muscle during Exposure to Fentanyl and Morphine

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Abstract
The effects of fentanyl on airway smooth muscle are not known. In this report the authors compare the effects of fentanyl and morphine on isolated canine tracheal smooth muscle. The contractile response of tracheal muscle strips to transmural electrical stimulation was attenuated by fentanyl (≥3 × 10−9 M) and morphine (≥3 × 10−7 M) in a dose-dependent manner; the attenuation was partially reversed by naloxone. Contractions induced by acetylcholine, histamine, and serotonin were reduced by prior treatment with fentanyl (≥10−7 M), but not morphine. The fentanyl-induced inhibition was not reversed by naloxone. In tracheal strips already contracted with acetylcholine, histamine, or serotonin, fentanyl produced relaxation, while, in contrast, morphine elicited a further contraction. In K+-contracted strips, fentanyl failed to produce relaxation. In tracheal strips sensitized in vitro by rabbit antiserum to bovine serum albumin, the addition of antigen (bovine serum albumin) produced a transient contraction, which was suppressed by prior treatment with fentanyl or chlorpheniramine. It may be concluded that fentanyl and morphine interfere with the release of acetylcholine from cholinergic nerves innervating tracheal smooth muscle; the interference appears to be associated mainly with activation of opiate receptors. Fentanyl, but not morphine, appears to possess antimuscarinic, antihistaminergic H1, and antiserotonergic actions. This suggests that fentanyl may be preferable for use in asthmatic patients.